The present invention relates to photographic flash equipment and particularly to an automatic flash which is insensitive to extraneous light.
Automatic flash equipment is known in which the light reflected from the object to be photographed during the flash discharge is detected by a photosensitive member which controls the charging of an integrating capacitor with a current proportional to the intensity of the detected light. The electric charge thus stored is compared with a preset value which corresponds to the optimum exposure for the photographic material employed. If this comparison indicates that the detected light has reached such a value, a special device interrupts the flash emission.
Before a photograph is made, the camera is set to a certain aperture whose value is determined by the guide number of the flash equipment for the film in the camera, with unchanging film sensitivity, and according to the camera operating instructions. As a function of the distance to the subject to be photographed, there then is determined the exposure time, which is calculated and determined by the instrument from the amount of reflected light.
One known arrangement for performing this function has the drawback that an extraneous flash which is discharged before actuation of the camera shutter, and thus before actuation of the triggering device of the flash equipment associated with that camera, will have the effect of causing the storage device of that flash equipment to discharge at the wrong time. A narrowing of the coverage angle of the photosensitive member can reduce its responsiveness to extraneous flashes. However, this will not completely eliminate the undesirable effects of such extraneous flashes. At the same time, the limitation of the photosensitive device viewing angle introduces a drawback in that only the reflections from a small portion of the image field are sensed.
An arrangement is also known having a control amplifier which is blocked until the output from a photocell actuated by the flash of the associated electronic flash releases it. This solution is complicated and requires a separate battery for the light meter and flash-limiting device or the simultaneous use of the battery of the electronic flash. With this arrangement it is impossible, however, to automatically operate the flash with energy supplied from the power mains without a special battery for the light meter and flash-limiting device.